1. Field of the Invention
This invention relates to solid state light source devices, and in particular, it relates to solid state light source device using light recycling to increase output brightness.
2. Description of the Related Art
Light emitting diodes (LEDs) have become a popular light source. However, the brightness of LED light sources is often insufficient for certain application areas such as large display devices, headlight for automobiles, stage lighting systems, etc. To improve the brightness of LED light sources, one approach is to increase the input power to each LED chip. But high power increases the demand on heat dissipation, because accumulated heat can cause the temperature of the LED chips to increase, reducing the light generating efficiency of the LED chips. This often results in an upper limit of the brightness of LED light sources. Moreover, large drive current can shorten the life of the LED devices and reduce their reliability. Therefore, the brightness of LED light sources cannot be increased in an unrestricted manner by increasing the drive current.
The light emitted by an LED device or a wavelength conversion material formed on the surface of an LED device typically has a near Lambertian distribution, i.e., its brightness is approximately uniform in all directions. Some techniques have been used to reduce the light distribution angle of a LED light source to increase its brightness. FIG. 13 illustrates a light source device 20 where small-angle lights A from the LED chip 21, i.e. light relatively close to a normal direction perpendicular to the surface of the LED chip, are outputted by an optical component 22 such as a lens, a reflector, an optical fiber, etc. Large-angle lights B, i.e. lights relatively farther away from the normal direction, are reflected by a spherical reflector 23 back toward the LED chip 21. The light reflected back to the LED chip 21 is scattered in all directions by the chip; of the scatter lights, the small-angle lights are output by the optical component 22 and the large-angle lights are reflected by the reflector 23 again. In this way, the large-angle lights are recycled, while the output lights have relatively small divergence angles (i.e. small etendue), resulting in increased brightness of the light source device 20.